High retention wood preservative composition

ABSTRACT

A wood preservative composition having deep penetration capability, leaving a clean surface and imparting high retention of active preservative within the wood, which consists primarily of (a) an organic wood preservative agent, (b) a hydrophobic agent, and (c) small amounts of an amorphous vinylic-type polymer, in a penetrating organic solvent. The preservative may be pentachlorophenol, an oxathiin compound or other preservative preferably of low mammalian toxicity. The hydrophobic agent may be fatty acids and their esters, fatty alcohols and paraffin waxes. The amorphous polymer may be a polystyrene, a polymethylmethacrylate, a polyvinylformal, an atactic polypropylene or other such amorphous polymer. The penetrating solvent may be most suitably chloroform, methylene chloride, trichloroethylene or liquefied petroleum gas, although others may be used. Solutions suitable for deep penetration pressure treatment are preferred. The active preservative penetrates and becomes immobilized within the penetrated wood microstructure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No. 417,404 filed Nov. 19, 1973, now abandoned.

FIELD OF THE INVENTION

This invention is directed to wood preservation primarily from biological attack using compositions causing the immobilization of active ingredient within the wood microstructure.

DESCRIPTION OF THE PRIOR ART

Contemporary systems for heavy duty preservation of timber (such as utility poles, piles, posts, bridge beams, glulams, lumber etc.) frequently employ pentachlorophenol (PCP) as a reliable heavy duty preservative. Application to leave a clean surface involves processes like "Cellon" (trademark) LPG impregnation or the methylene chloride solvent treatment to drive the PCP into the wood providing a reasonably clean surface requiring no seasoning. However material treated with PCP by these processes, suffers from disadvantages such as loss of PCP from the wood (sublimation) and low water repellency and weather resistance. Both disadvantages result in lowering of service life when compared with wood treated by the older conventional PCP-oil-borne systems, and also in limitations to use of the treated wood in closed poorly ventilated areas, e.g. basements. (The PCP-oil-borne systems have the major disadvantages of wood discolouration, oily unpaintable surfaces stickiness and dirt retention.)

These disadvantages (using the so-called clean processes) can be partially solved by raising the amount of preservative incorporated into the wood thus retaining the concentration level above or close to the effective threshold value even after loss of some preservative resulting in an acceptable service life. Adequate water-repellancy and PCP retention, and elimination of the health hazard due to vapours of PCP, can be realized by additional painting or top-coating of the wood surface. Such additional treatments (use of excess PCP and/or top-coating) considerably increase the cost of treated wood and in many cases are not economical. Heavy loadings of polymers and/or resins have been incorporated in PCP preservative compositions to completely seal the wood surface as in British Patent Specification No. 1,281,911 Blunt et al. However, loss of penetrability and cost render this unacceptable in many applications. See Example 6 below.

It would be desirable to have a clean heavy duty wood preservative system having penetration of preservative equivalent to the methylene chloride-PCP system, and water-repellency and service life at least as good or better than the PCP-oil-borne systems.

SUMMARY OF THE INVENTION

According to the invention, a wood preservative composition is provided having deep penetration capability, imparting a clean surface and good service life to the wood substrate. The composition comprises:

a. an organic wood preservative agent;

b. a hydrophobic agent selected from fatty acids and their esters, fatty alcohols and various waxes, suitably having at least 10 carbon atoms in the longest chain in the molecule;

c. an amorphous vinylic-type polymer in amounts of up to about 30% by weight based on total solids; and

d. a penetrating organic solvent for (a), (b) and (c).

In the drawings,

FIG. 1 is a graph showing results of accelerated sublimation tests;

FIG. 2 is a graph showing the hydrophobicity (contact angle) on treated surfaces;

FIGS. 1a and 1b are photomicrographs at 455× of a wood microstructure penetrated with PCP alone, before and after vacuum exposure;

FIGS. 2a and 2b are photomicrographs at 455× of a different wood microstructure penetrated with the formulation of this invention before and after vacuum exposure.

The preservative should be highly toxic to microorganisms which attack wood, and is suitably pentachlorophenol, an oxathiin antimicrobial, tributyl tin oxide or other organic biocide. The composition will preferably include from about 1 to about 6% w/v of preservative, although slightly more than this could be operative (up to the limit of solubility).

The hydrophobic agent is a water-insoluble solid or semisolid from fatty acids, fatty acid esters, fatty alcohols and various waxes. These acids, esters, fatty alcohols, waxes and mixture thereof should be soluble in the solvent to at least about 0.5% w/v, preferably about 2-4%. There is usually no advantage in including more than about 5% although up to the limit of solubility would be operative Examples include decanoic acid, lauric acid, palmitic acid, stearic and oleic acids, octadecanol, ethyl laurate, methyl stearate, propyl stearate, benzyl laurate, phenyl laurate, and paraffinic waxes. Those hydrophobic agents having higher melting points, such as lauric acid (44° C), palmitic acid (63° C), stearic acid (70.1° C), paraffin waxes etc. are preferred to those with lower melting point such as nonanoic acid (15° C), decanoic acid (31.5° C) or oleic acid (16.3° C). Paraffin waxes have been tested and provided the same degree of water repellency as the fatty acids with higher melting points (>44° C). Waxes are usually the cheapest, although crude mixtures of acids or esters would also be low-cost agents.

The vinylic-type polymer must be amorphous and soluble in the same solvent as the other components to at least about 0.2% w/v, preferably about 0.3 to 1%. The amount of polymer will normally not exceed about 30% by weight of total solids in the composition. As low as about 3% of the solids would be operative. A preferred range is about 5 to 20% of the solids. The main function of the polymer is to immobilize or reduce loss of preservative while at the same time increasing water repellency. Thus the vinylic polymer will be highly compatible with the preservative. The degree of polymerization of the polymer is selected so that the polymer has sufficient solubility in the organic solvent. The amorphous nature of the polymer is of primary importance in defining the suitability of this component. The amorphous condition enables effective and uniform enmeshing of the preservative and the hydrophobic agent (usually both crystalline) among the polymer chains when deposited in the wood. A crystalline polymer, after solvent removal, would form areas of polymer separate from the other components, and would not have the required protective function. Examples can be selected from the group including polystyrenes, polymethacrylates (e.g. methylmethacrylates or butylmethacrylates), atactic polypropylenes, polyvinylformals, and other amorphous vinylic-type polymers.

The common solvent for dissolving all three main components into one solution, is an organic solvent of lipophilic nature i.e. a fat solvent. Preferred are the highly halogenated lower aliphatic hydrocarbons with low boiling point (less that 100° C) and preferably which are non-flammable, such as tetrachloromethane (carbon tetrachloride), trichloromethane (chloroform), bromochloromethane, 1,1,1-trichloroethane, bromodichloromethane, trichloroethane, 1,2-dichloromethane (methylene chloride) and mixtures thereof. Those solvents with higher boiling point (more than 100° C) and preferably non-flammable (e.g. trichlorethylene, tetrachloroethylene) can be used with advantage in applications like spray, brush or dip treatments. Also a highly volatile liquefied petroleum gas (LPG), usually with cosolvent, can be used as in the "Cellon" (trademark) process.

The solvents ability to dissolve all three components into one solution is the main criterion for its selection. Non-flammability, though preferred, is not an essential feature of the solvent. Where deep pressure treatment of large forest products (such as poles or square timber) is required, the solvents should have low polarity or be non-polar (with dielectric constant<15.0) in order to penetrate fast and deep into wood while carrying all of the additives and they should have a low boiling point (<100° C) because almost full recovery of solvent is necessary. In non-pressure treatments like dip, brush or spray treatments or treatments of smaller forest products, the requirements for polarity and boiling point of solvent are less strict (solvents with higher polarity and higher boiling point can be used in this case). Boiling point and polarity are not necessary criteria for solvent definition. Such other solvents can be aromatic, for example, benzene, toluene, or xylene. These aromatic solvents dissolve PCP, fatty acids, paraffin waxes and polystyrene as well. But they could not be used with e.g. polyvinylformal as this polymer is not solubilized by them. However polyvinylformal could be used in chloroform solution. On the other hand, aliphatic hydrocarbons, e.g. Varsol (trademark) while solvents for PCP, fatty acids and paraffin waxes, do not dissolve the polymers.

The preservative composition can be applied by various methods used in the industry; for example by impregnation of square or round timbers (under pressure) or by dip, spray or brush treatment of lumber or fabricated structures. Any impregnation method employed for an oil-free system can be used; thus in addition to LPG-cosolvent systems, the methylene chloride treatment (MCHP) is also operative.

All three components in the preservative solution penetrate into the wood during application, and after the evaporation of solvent the composition changes into a homogeneous mixture of preservative and hydrophobic agent, both immobilized or retained in a web, film or matrix structure of polymer. The penetrated wood is left with a clean surface. Thus there is formed in the wood a "complex network of closed microsegments" in which all penetrated cells in the wood are sealed by a continuous system of barriers. Each barrier is protecting each closed microsegment of the wood in three ways i.e. against (1) blooming or sublimation loss of preservative, (2) wetting and leaching of the preservative, and (3) biological attack and degradation. The hydrophobic agent reliably increases the water-repellency but it cannot adequately immobilize the preservative in the wood microstructure. The polymer on the other hand forms impermeable barriers (even when in low concentration) effectively limiting sublimation loss and confining the preservative within the cell or closed microsegment -- but in the small concentration used is unable to bestow adequate water-repellency on its own.

If the hydrophobic agent was omitted, an increase of polymer component would be required. However, because the polymer has a high molecular weight compared to the hydrophobic agent, a treating solution containing larger amounts of polymer would penetrate less rapidly into wood. It should be emphasized that the excellent penetrability of the oil-free systems (either MCHP system or Cellon system or others as in the present invention) to carry PCP deeply into wood is one of the major advantages of these systems. Reduction of penetrability due to polymeric ingredients in significant concentrations would make the preservative system less efficient. Hydrophobic agents according to this invention are low molecular compounds which do not reduce the penetrability of the solutions significantly (neither do the low concentrations (up to about 1% w/v) of amorphous polymer).

A suitable amount of preservative deposited in the wood would range from about 0.05 to about 2.5 lbs. (total solids)/cu.ft. for effective preservation. Somewhat more or less than this may be useful in certain cases.

The invention is illustrated by the following Examples.

EXAMPLE 1 The Accelerated Sublimation Test

In order to determine the influence of chemical components in the preservative composition on loss of preservative (PCP) under accelerated sublimation conditions, three solutions have been prepared, separately, in carbon tetrachloride as a solvent (in percent w/v).

I. solution: PCP (3.5%) as a preservative.

Ii. solution: PCP (3.5%) and stearic acid (3.5%) as the hydrophobic agent.

Iii. solution: PCP (3.5%) stearic acid (3.5%) and polystyrene (0.7%) as the organic polymer.

The same volume of each solution (0.07 ccm/sq. in.) has been poured on the surface of glass template and the solvent evaporated at room temperature leaving solid deposits of each sample. Then these deposits of the three different preservative compositions (I-II-III), in which the amount of preservative (PCP) was the same, were exposed to vacuum at room temperature in order to accelerate the loss of components. The loss of weight of each single deposit was checked periodically and is expressed in FIG. 1 in percent of original weight of preservative (PCP).

This experiment clearly shows that the admixture of organic polymer along with the hydrophobic agent allows a loss of PCP of only about 36%, which is a 63% reduction of PCP sublimation compared to the control sample. When PCP is protected by no additive it has evaporated under same conditions to the extent of 99%.

The reduction of PCP sublimation on account of the presence of 0.7% of polymer (polystyrene) amounts to 30%, while the hydrophobic agent (stearic acid) in a much higher concentration (3.5%) than the organic polymer shows a reduction of PCP sublimation of only 34% from the control (all percentages are as shown in FIG. 1). The experimental evidence proves the high efficiency of the organic polymer component in very low concentrations in reducing the preservative (PCP) loss due to evaporation.

EXAMPLE 2 The Hydrophobicity of Wood Treated by Preservative

The same solutions of preservative compositions (I-II-III), as in Example 1 have been used for impregnation of red pine wood samples in order to determine the effect on hydrophobicity of wood. After the samples of wood have been fully saturated by solutions I-II-III, the solvent was then evaporated at room temperature during the next 24 hours, leaving solid deposits of the components in the wood. Measurements of contact angles of the surface of water drops on pertinent wood samples were made to show the relative hydrophobicity. The sooner the water soaks in the surface of wood (contact angle 180° ) the lower the hydrophobicity of wood and vice versa. FIG. 2 shows clearly that wood treated by PCP alone, soaked water readily (within 40 seconds), while the wood treated by the preservative composition comprising hydrophobic agent and amorphous organic polymer (sample III) did not allow water to soak into the surface completely even after 50 min. The hydrophobic agent (stearic acid in sample II) itself improved significantly the hydrophobicity but the water soaked into the wood after more than 16 min.

EXAMPLE 3 Microscopic Tests of Preservative Composition

In order to illustrate further the protective function of the polymer in the mixture of preservative with hydrophobic agent, photomicrographs have been taken of preservative compositions deposited in thin layers (from solution I-II-III, as in Example 1.) In the solid deposit of preservative from solution I (PCP only) and from solution II (PCP and stearic acid one/one respectively), the hydrophobic agent (stearic acid) is seen to partially cover the crystals of preservative (PCP). The same picture can be seen when the organic polymer is added to solution II in order to make solution III and dried at the beginning of an evaporation test. But the major effect or protective function of the polymer (polystyrene) present in solution III is to reduce the loss of preservative, and this is seen after the accelerated evaporation test as in Example 1 has been completed. At this point (after 70 hours under vacuum) when the control sample from solution I (PCP only) protected by no additive has 99% disappeared, the sample from solution II (PCP and stearic acid) shows that PCP crystals have also disappeared from major part of sample.

However, the sample in which PCP with stearic acid has been protected against evaporation by further admixture of 0.7% (w/v) of amorphous polymer (polystyrene), demonstrated clearly the protection of PCP crystals which were partially embedded in a transparent layer of polystyrene (along with particles of stearic acid).

Comparison of the photomicrographs showed the important function of the polymer as a necessary component in the preservative composition to protect the preservative (PCP) against loss due to sublimation.

EXAMPLE 4 Soil Block Tests

Tests were carried out to demonstrate the toxicity of treated wood samples to wood-destroying fungi i.e. to show that the PCP is not rendered ineffective. The composition of the present invention was compared with PCP itself in a standard test (AWPA-MIO) against two wood-destroying fungi Poria vaporaria and Coniophora cerebella using white pine.

There was little difference in toxicity between PCP and the composition of the present invention (e.g. 3.5% PCP, 1% stearic acid and 0.7% polystyrene) although a slight benefit for the latter appeared at low retention levels. Statistical analysis showed no significant difference between PCP itself and this particular formulation at the tested retention levels of 0.05, 0.10, 0.25, 0.75 and 1.75 lbs. PCP/cu. ft. However the present invention would bestow much prolonged effectiveness over PCP alone.

EXAMPLE 5

The following formulation was prepared:

3.5% w/v PCP,

0.8% paraffin wax, M.P. 51.5° C and

0.6% polystyrene,

in carbon tetrachloride as solvent. Samples of Western Red Cedar, 1 inch by 3/4 inch by 1/2 inch, were impregnated with this preservative for 1 hour under a vacuum of 25 inches of mercury, and subsequently air-dried.

In the water-repellency test, the contact angle on the treated sample was initially similar to line III in FIG. 2. After 37 min. the contact angle had reached 180°. Considering the lower percentage of hydrophobic agent used, this is a very acceptable water-repellency.

The formulation of the present invention has been tested on various wood species and it has been shown that the wood remains undiscoloured having a natural appearance, that the surface has good water repellency, and that toxicity and PCP retention remain high for prolonged service life.

EXAMPLE 6

For comparison with the Blunt et al. British patent specification No. 1,281,911, two formulations were made up as follows to a constant PCP level. (Percents are on a weight/volume basis). It was necessary to heat the Blunt et al formulation to 55° C on a water bath to obtain dissolution.

    ______________________________________                                         Component      Present    Blunt et al                                          ______________________________________                                         PCP %          4.5        4.5                                                  Polystyrene %  1          4.5 (100% of PCP)                                    Paraffin wax % 4.5        --                                                   Escorez resin % (Esso)                                                                        --           9% (200% of PCP)                                   Solvent        Chloroform Solvent Naphtha                                      ______________________________________                                    

The main difference between these two types of formulations is the ability to penetrate wood (the present one is designed for deep penetration for heavy duty, while Blunt et al's is designed for surface blocking treatment). To accentuate penetration, both formulations were tested in pressure treatments carried out simultaneously on spruce wood samples (five samples for each formulation). The samples 1 × 1 × 12 inches were treated at 20 psi pressure for 2 hours while immersed in the preservative liquids. After the treatment, the samples were cross cut in the center and the preservative liquid penetration marked and measured in the transverse direction. A second series of pressure treatments was carried out as before but for 4 hours, and the penetration again marked and measured at the centers (where not affected by end penetration). The results were as follows.

    ______________________________________                                         Average Penetration Depth (Inch) in Spruce                                     Present          Blunt et al                                                   Two hours                                                                               Four hours  Two hours   Four hours                                    ______________________________________                                         0.2      0.3         0.07        0.1                                           ______________________________________                                    

The penetration of the Blunt et al formulation was only about one third that of the present formulation. The sample cross sections were carefully examined after the solvent dried off and the PCP penetration was observed to be the same as the solvent for the Rak formulation, but PCP was left behind the solvent penetration for the Blunt samples. This degree of penetration for the Blunt et al formulation would render it unacceptable for commercial pressure treatment use for which the present formulation is primarily designed. It is clear that the Blunt et al formulation was designed only for surface pore blocking and improved paint adhesion, not for deep penetration of the wood.

In order to meet American Wood Preserver's Association and Canadian Standards Association 080 specifications for pressure treatment penetration of preservative, the penetration must be substantially equivalent to that of the "Dow Process" PCP-in-methylene chloride system (see AWPA Proceedings, Vol. 68, 1972, page 148 etc.) A preservative uptake experiment was carried out by immersing samples of white spruce in the preservative solutions at atmospheric pressure, the preservative solutions being (a) PCP in methylene chloride (5%), "Dow Process" preservative, (b) PCP (5%) + paraffin wax (3.5%) + polystyrene (1%) in methylene chloride, i.e. present preservative. The uptake of preservative solution (volume) was measured and plotted against time of immersion for (a) and (b) solutions and the curves were seen to be substantially identical. Thus the present formulation (b) will meet the penetrability standards (but the Blunt et al formulation would not).

EXAMPLE 7 Comparative Penetration Test by Solution Uptake

Sorption and diffusion of solution in wood without pressure conditions helps to carry the solutions further into wood (even after a main preservative treatment by a high pressure process). Faster uptake of preservative solution indicates better penetrability of the solution and results in deep preservative penetration in wood.

Tests were carried out under non-pressure conditions, on spruce blocks of size 1.05 × 1.05 × 1.05 inch, with 10 replicas for each tested solution. Since the specific gravity of the test solutions varied, solution uptake was measured as volume (not weight) of the solution taken up by the blocks. Average values of solution uptake were determined.

The following compositions were tested: (solutions with % on weight/volume basis)

1. 4.5% pcp in chloroform

2. 4.5% pcp in methylene chloride

3. 4.5% pcp, 3.5% stearic acid, 1.0% polystyrene in methylene chloride

4. 4.5% pcp, 3.5% stearic acid, 1.0% polymethylmethacrylate in chloroform

5. 4.5% pcp, 3.5% stearic acid, 1.0% polyvinylformal in chloroform

6. 4.5% pcp in pole oil

Results of solution uptake by volume of air dried spruce samples are shown in Table 1.

a. The non-pressure solution uptake during 24 hour period clearly indicated the variation between fast and slow penetration of the preservative compositions.

b. Preservative compositions Nos. 1, 2 and 3 have almost identical rates of solution uptake and showed the greatest penetration.

c. Preservative compositions Nos. 4 and 5 have a slightly slower rate of solution uptake, but they belong, according to the trend of solution uptake between 5 and 24 hours exposure, to the same group of deeply penetrating preservative solutions as 1, 2 and 3 with relatively high rates of penetration.

d. The typical oil solution of pcp #6 penetrated into wood at a significantly slower rate than the #1-#5 preservative compositions. These #1-#5 compositions showed, after 24 hours exposure, 27 to 46% higher solution uptake by volume than the oil solution.

e. Staining of penetrated sections revealed the pcp had fully penetrated with the solvent for #1-#5, while for #6, pcp penetration was relatively superficial.

                  TABLE 1                                                          ______________________________________                                         Average Volumes of Preservative Solution Taken up by                           One Inch Cube Spruce Samples                                                                Preservative Solution Number                                      Time of Exposure                                                                              1      2      3    4    5    6                                  hours    mins.     (ml)   (ml) (ml) (ml) (ml) (ml)                             ______________________________________                                         1        25        1.00   1.03 1.01 1.15 1.15 --                               2        25        1.25   1.24 1.26 1.33 1.22 1.30                             5        30        1.62   1.62 1.61 1.62 1.48 1.50                             8        30        1.93   1.94 1.93 1.86 1.72 1.65                             24       30        3.00   2.98 3.01 2.70 2.60 2.05                             ______________________________________                                    

EXAMPLE 8 Immobilization of Preservative in the Wood Structure

This Example illustrates the difference between immobility and high retention of preservative deposited in wood by the composition of this invention, and preservative deposited without any additives from the standard solution in methylene chloride (Dow Process).

Two homogeneous samples of spruce wood, 2 × 2 × 18 inch each, containing sapwood, were treated with two different solutions:

Sample A: treated with 4.5% w/v of PCP in methylene chloride, corresponding to commercial "Dow Process".

Sample B: treated with 4.5% w/v of PCP, 4.5% w/v stearic acid, 1.0% w/v polystyrene in methylene chloride solution.

After pressure treatment (at 120 psi for 7 hours, at room temperature) the samples were taken out of the retort, cross-cut and penetration of PCP was detected by application of stain (in the form of a spray) specific for PCP detection, known as "Penta-Check" (trademark) according to AWPA Standard A3-68. The depth of penetration on cross-sectioning in both samples A and B was approximately 0.4 inch. Similarly to Example 7, the penetrations for solutions A and B under pressure were equivalent i.e., the additives of the invention did not significantly retard penetration in either solution uptake or pressure treatment.

After the PCP penetration was detected in the sapwood area in both samples to approximately in the same depth, the stained surface of the cross-section was removed from both samples by additional cutting away of a slice of the cross-section to provide unstained surfaces of the treated wood.

From both samples, microsections were cut from the wood tissues, approximately 0.35-0.37 inch from the surface in the radial direction, i.e. within the area, where the PCP was positively detected by previous staining. Numerous microscopic sections (transverse) were made from both samples (A and B) separately. From each of both groups of microsections, typical sections were again microscopically stained with a Silver-Copper complex (which is the basis of the "Penta-Check") to detect again PCP in the microsections. Other typical unstained microsections were mounted into microscopic slides and without any staining examined microscopically. On the viewed microsections of treated wood typical spots were selected where the cell obviously contained significant deposits of PCP, and photographed, at the same magnification. Photographed microsections from sample A and B were then carefully removed from the slides, gently dried off by a touch of absorbent paper at the corner of the microsections, and transferred into a vacuum desiccator by a micromanipulator. The desiccator was then closed and very slowly evacuated. When the vacuum reached 29.5 inch Hg, the desiccator was sealed and the microsections left for 7 days (exactly 164 hours). Then the desiccator, still at 27 inch vacuum, was slowly filled with air, opened and the microsections transferred onto glass slides and mounted for microscopic examination. This exposure under the same vacuum conditions (29.5 - 27 inch Hg) for 7 days gave accelerated sublimation of PCP. The accelerated vacuum test is considered as an accurate simulation of the effect of ordinary atmosphere for an extended time. The microscopic slides were carefully examined, the same spot of each microsection was found (as photographed before vacuum exposure) and rephotographed (at the same magnification) for comparison.

Two pairs of photomicrographs are shown as FIGS. 1a and 1b, and as FIGS. 2a and 2b, being typical of observations of as many as 50 microsections. The first pair, FIGS. 1a and 1b, depict the same microstructure, at a magnification of 455 times, impregnated with PCP before 1a and after 1b the vacuum exposure. The second pair of photomicrographs 2a and 2b, also at 455×, are for PCP + additive formulation of the present invention and depict the same cells of the spruce microstructure before 2a and after 2b the 164 hour vacuum exposure.

The identical cells shown on microsections a and b of FIGS. 1 and 2, are numbered and marked by letters for comparison. During handling of microsections between the first photographing and the second, the microsections were accidentally turned upside down so they formed mirror images. However, the same cells and lumina are shown.

OBSERVATIONS (EXAMPLE 8)

The microsections of spruce treated under the same treating conditions with two different preservative solutions showed the same penetration depth.

In FIG. 1a cells designated 1, 3, 4, 5, A, F and G have crystals, whiskers or deposits of PCP associated therewith. In FIG. 1b, the same cells are devoid of PCP due to the vacuum exposure.

In FIG. 2a, cells 1, 2, 3, 4, 5, 6, 7, A, B, C and D have deposits which include PCP associated therewith. In FIG. 2b, cells 1, 2, 3, 4, 5, 6, B, C and D still have substantial deposits including PCP after the vacuum treatment. Only two cells, 7 and A, have lost visible deposits. The PCP-containing deposits are visible between the cells or as a layer around the cell lumen.

Thus PCP alone had disappeared after vacuum exposure FIG. 1b, while PCP plus the polymer and water-repellent additives substantially withstood the same vacuum exposure. The new formulation caused immobilization and high retention of the active preservative.

Another important feature of the new formulation is the regular distribution of PCP enmeshed with additives around the cell lumina. Microscopic staining showed that PCP was evenly distributed around the cell lumina in the preservative deposits in the cells. PCP does not separate or migrate from the additives in the microstructure of the wood. On the other hand, PCP without these additives, was deposited on the cell walls in individual spots (in form of crystals, see FIG. 1a) rather than being deposited on the cell lumen in a continuous layer (as shown in FIGS. 2a and 2b).

The microscopic sections treated with PCP + additives also showed considerable water repellency (as proven earlier by tests of water-repellency rating). As seen in FIGS. 2a and 2b, those cells containing deposits of preservative around the lumina are also darker. It is evident the preservative prevented the water (used for mounting of the microsection) from entering into the lumen so that an air bubble was trapped in the lumen and visible darkening of the lumen resulted. When no preservative (PCP + additive) was present (such as in FIG. 2b, in cell 7 and A) water entered the lumen and visibly clear lumen resulted. It is evident that the microsections with PCP only (such as in FIG. 1a) contained preservative in form of crystals which were separate from each other on the cell wall in the lumina of cells, and because these crystals are not highly water repellent, water entered into all lumina (and a clearer picture resulted).

Recently more interest is being shown in biocides (fungicides, bactericides) of low mammalian toxicity. Oxathiin derivatives have been developed as systemic plant fungicides (see inter alia U.S. Pat. No. 3,249,499). Various oxathiins and other carboxanilides having fungicidal properties are described by R. J. W. Cremlyn in International Pest Control 15(2) 1973 pages 8 - 11. The structure ##STR1## is common to these fungicides. The double bond is part of an appropriate ring structure, usually a heterocyclic ring. Several of these carboxanilides are on the market as seed dressings or systemic fungicides against rusts, smuts and bunts of cereals and some ornamentals. These fungicides generally have low mammalian toxicity.

Preliminary tests indicated that oxathiin derivatives (deposited from methanol solutions) would have a preservative effect in wood subject to decay by fungi (see R. S. Smith in Environment Canada -- Bimonthly Research Notes 26(3) 1970 page 24).

The following examples illustrate the use of these derivatives in the wood preservative system of the present invention. The following two compounds were used in the tests:

D-18 or carboxin = 2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxathiin

D-20 or oxycarboxin = 4,4-dioxide analog of D-18

EXAMPLE 9 Leaching Resistance Test

Comparable samples of spruce sapwood were saturated with four different preservative solutions as follows:

Solution I: 5% w/v D-18 in chloroform

Solution II: 5% w/v D-20 in chloroform

Solution III: 5% w/v D-18

1.4% w/v paraffin wax

1.0% w/v polystyrene in chloroform

Solution IV: same as III but with 5% w/v D-20.

uptake of preservative was calculated from the weight increase. Chloroform solvent was removed from the samples by air drying followed by drying in the oven at 105° C for 4 hours. Each sample was leached with a standard volume of distilled water at room temperature. Every 2 hours the water surrounding each sample was removed for spectrophotometric measurement and was replaced by another standard volume of fresh distilled water. Total leaching time was 140 hours. The concentration of D18 and D20 in the leach water was determined by comparing specific absorbance in UV light with the absorbance of known concentrations of D18 and D20 in water. The leached amount of D18 and D20 was recalculated as a percent of the orginial amount impregnated into the samples before leaching.

Table 2 shows that the samples treated with both preservative solutions containing the additives of this invention were significantly more leach-resistant than their counterpart samples treated with the D18 or D20 solutions without additives. The additives increased the leaching resistance of wood treated with D18 by 51-57%, and the wood treated with D20 by 17-27%. These figures correspond well with the relatively higher water solubility of D20 (1000 ppm) compared to the lower solubility of D18 (170 ppm).

The concentration of additives used in this test was not very high and could be increased according to the concentration limits for the additives defined above. The penetrability was not retarded by the additives.

                  TABLE 2                                                          ______________________________________                                         Cumulative Percent Preservative Leached from Wood                              Hours of                                                                       Exposure D18    D18+Additives                                                                               D20  D20+Additives                                ______________________________________                                         10       14      8           10   17                                           30       27     14           38   28                                           70       43     21           54   41                                           140      56     27           61   51                                           ______________________________________                                    

EXAMPLE 10 Effectiveness against Decay Fungi

The fungicidal activity of these compositions was determined in an accelerated experiment with the wood-rotting basidiomycetes Lenzites trabea (S644), Coniophora puteana (A302) and Poria monticola (A384) as test fungi. Small cross-the-grain sections of spruce wood (Picea glauca, a refractory species) were cut 40 microns thick on a microtome. All treatment specimens (0.5 × 0.5 inch) were cut from the same block of wood and were therefore homogeneous in nature. Wood specimens were treated to different retention levels with the active ingredients D18 or D20 with or without the additives. Two of each treatment series were placed on sterilized glass microscopic cover slips (22 mm²) which were then deposited upon cultures of actively growing decay fungi in Petri dishes. Cultures were grown on a 2% malt extract, 2% agar medium. Two untreated specimens were included in each culture dish as controls. Treatment series were 0.1, 0.5 and 1.75 pcf. Incubation was for 19 days at 27° C. Each test was done in duplicate. Evaluation of the treated samples was made using a stereoscopic microscope (× 10.5 magnification). The percentage of the surface area of each specimen colonized by the test fungus was determined. The smaller the colonized surface area of each wood specimen, the more efficient the preservative composition used for specimen treatment.

                  TABLE 3                                                          ______________________________________                                         Average Percentage of Wood Area Colonized by Test                              Fungi after 19 Days Incubation at 27° C                                                   Retention of solids                                                            in preservatives                                                                             non-                                           Test              (pcf)         treated                                        Fungus   Preservative 0.1    0.5  1.75  controls                               ______________________________________                                         Lenzites                                                                       trabea   D18          25*    0    0     100                                             D18+additives                                                                               25*    0    0     100                                             D20          50     0    0     100                                             D20+additives                                                                               20     0    0     100                                    Coniphora                                                                      puteana  D18          30     5    5     100                                             D18+additives                                                                                5     2.5  0     100                                             D20          40     10   10    100                                             D20+additives                                                                                8     2.5  0     100                                    Poria                                                                          monticola                                                                               D18          40*    0    0     100                                             D18+additives                                                                               15*    0    0     100                                             D20          50     15   10    100                                             D20+additives                                                                               15     5    5     100                                    ______________________________________                                          *Mycelia in these cases extended over the top of the treated specimens bu      did not colonize all of the substrate underneath.                        

Inclusion of the additives in the compositions studies did not reduce the effectiveness of the fungicides when compared to the compositions without additives (in most cases showed slight improvement -- see Table 3). Coniophora puteana, which was generally more resistant to D18 and D20 than the other two fungi, grew less on the specimens treated with the fungicides containing the additives than on those specimens treated with the fungicides without the additives. This was particularly noticeable at the lowest retention level of 0.1 pcf of the chemicals.

An increase in the effectiveness of D20 due to the additives was, in addition, obtained in the tests with Poria monticola and Lenzites trabea (Table 3). Growth on specimens treated with D18 with or without additives at 0.1 pcf resulted, for the most part from mycelia growing over the specimens rather than on them.

EXAMPLE 11

Two series of 5 wood samples were treated under comparable conditions with two preservative formulations:

5% (w/v) D18 in chloroform and

5% (w/v) D18 with 1.4% wax and 1% polystyrene in chloroform solution.

Initial preservative retentions were in the range 1.48-1.52 mg/cm³. After solvent removal by slow air drying and a short period of oven drying both series of samples were exposed to leaching in water under the same conditions (time of exposure, temperature and volume of water for leaching). The residual amount of preservative left in the sample was determined from the difference between the original retention of the preservative and its amount present in the leaching water defined spectrophotometically. After leaching the samples were further tested for toxicity against a wood-decaying fungus in a modified standard method of testing wood preservatives by laboratory soil-block cultures. Five untreated controls and five samples from each preservative series were put into soil jars on wooden feeder blocks inoculated with a standard test fungus Poria monticola. Each of the five culture jars contained one untreated control, one specimen treated with D18 and one specimen treated with D18+additives. Jars were located in an incubation room maintained at 80° F and 70% R.H. and were opened one by one in five consecutive time intervals, after 25 - 32 - 39 - 46 and 65 days incubation. Wood specimens taken from the jars were oven dried and the weight loss due to decay calculated. The results are summarized in the following Table 4.

                  TABLE 4                                                          ______________________________________                                         Cumulative Percent Weight Loss Due to Decay                                                 Untreated                                                         Days of Incubation                                                                          Control    D18     D18+Additives                                  ______________________________________                                         25            5          2      1.5                                            32           14          4      2                                              39           --          6      2                                              41           32         --      --                                             45           --         --      2.5                                            46           35         10      --                                             65           50         21      3.5                                            ______________________________________                                    

This experiment proves that the additives play an important role in increasing leaching-resistance of the active preservative component in treated wood. The formulation of the invention extends the toxicity of treated wood to decay fungi, thus prolonging the service life.

EXAMPLE 12 Test of Solubility of Oxathiins in Various Solvents

Table 5 is a solubility chart summarizing a list of organic solvents solubilizing oxathiins and the two additives which can be applied in the same solution.

                  TABLE 5                                                          ______________________________________                                         Solubility Chart                                                                           oxathiins   additives                                              Solvent       D18      D20      wax  polystyrene                               ______________________________________                                         Methylene chloride                                                                           +        +        +    +                                         Chloroform    +        +        +    +                                         Benzene       +        +        +    +                                         Toluene       +        +        +    +                                         Xylene        +        +        +    +                                         Propanol      +        -        -    -                                         Carbon tetrachloride                                                                         +        -(+)     +    +                                         Perchloroethylene                                                                            +        -(+)     +    +                                         Water         170 ppm  1000 ppm -    -                                         ______________________________________                                    

Tests with the formulations in methylene chloride and in chloroform solutions indicated the solutions were stable in the presence of iron, i.e. could be handled in iron or steel equipment. 

I claim:
 1. A method of increasing and prolonging the immobilization of preservative in wood on treating wood with deeply penetrating wood preservative solutions said penetrated preservative tending to migrate and become depleted on prolonged service, comprising:a. incorporating in the wood preservative solution in a deeply penetrating organic solvent (i) a hydrophobic agent selected from the group consisting of fatty acids and their esters, fatty alcohols and paraffin waxes in amounts of from about 0.5% up to about 5% weight/volume based on the solution, said fatty acids and alcohols having at least 10 carbon atoms in the molecule; and (ii) an amorphous vinylic-type polymer in amounts of at least about 0.2% w/v up to about 1% w/v based on the solution, said polymer being soluble in the solution; and b. penetrating the wood with the modified preservative solution said modified solution having deep penetrability substantially equivalent to that of the initial solution and evaporating the solvent to leave a clean wood surface.
 2. The method of claim 1 wherein the wood preservative is selected from the group consisting of pentachlorophenol, an oxathiin biocide and tributyl tin oxide.
 3. The method of claim 1 wherein the polymer is selected from the group consisting of soluble polystyrenes, soluble polymethacrylates, soluble atactic polypropylenes, and soluble polyvinylformals.
 4. The method of claim 1 wherein the amount of polymer ranges from about 3% to about 30% of the weight of total solids.
 5. The method of claim 3 wherein the amount of polymer is within about 5% to about 20% of the weight of total solids.
 6. The method of claim 5 wherein the polymer is polystyrene.
 7. The method of claim 1 wherein the wood preservative is pentachlorophenol.
 8. The method of claim 1 wherein the wood preservative is an oxathiin compound biocide.
 9. Wood deeply penetrated with a preservative composition and having a clean surface, wherein the preservative composition comprises:a. an organic wood preservative agent which tends to migrate and become depleted on prolonged service; b. a hydrophobic agent selected from the group consisting of fatty acids and their esters, fatty alcohols and paraffin waxes in amounts effective to bestow water-repellency yet not significantly decrease penetration; and c. an amorphous vinylic-type polymer in amounts of from about 3% to about 30% of the weight of total solids in said composition; components (b) and (c) being deeply penetrated with (a) and serving to immobilize (a) within the wood for prolonged service.
 10. Wood penetrated with a preservative composition as in claim 9 wherein the wood preservative agent is selected from the group consisting of pentachlorophenol, an oxathiin biocide and tributyl tin oxide.
 11. Wood penetrated with a preservative composition as in claim 9 wherein the polymer is selected from the group consisting of soluble polystyrenes, soluble polymethacrylates, soluble atactic polypropylenes, and soluble polyvinylformals.
 12. Wood penetrated with a preservative composition as in claim 9 wherein the amount of hydrophobic agent is not significantly greater than the amount of preservative agent in said composition.
 13. Wood penetrated with a preservative composition as in claim 11 wherein the amount of polymer ranges from about 5% to about 20% of the weight of total solids of said composition.
 14. Wood penetrated with a preservative composition as in claim 13 wherein the polymer is polystyrene.
 15. Wood penetrated with a preservative composition as in claim 9 wherein the wood preservative agent is pentachlorophenol.
 16. Wood penetrated with a preservative composition as in claim 9 wherein the wood preservative is an oxathiin compound biocide. 